Developments in the diagnostic procedures for von Willebrand disease

ECMO produces very rapid changes in primary hemostasis detected by PFA-200 during lung transplantation: An observational study

BACKGROUND

The pathology of primary hemostasis is a common complication of extracorporeal membrane oxygenation (ECMO) support. Scientific data describing its changes in patients on short-term ECMO support and the ability and speed of the restoration of its functions are limited.

AIMS

The aim of this study was to describe the pathology of primary hemostasis induced by short-term ECMO support and its development over time using PFA-200, ROTEM platelet, and von Willebrand factor (vWF) analyses.

METHODS

In patients undergoing lung transplantation surgery using intraoperative veno-arterial ECMO support, blood samples were analyzed using the following tests: PFA-200, ROTEM platelet tests, vWF antigen, ristocetin cofactor (RCo), and collagen-binding protein (CB) before, during, and after ECMO support.

RESULTS

Blood samples from 32 patients were analyzed. All 3 PFA-200 tests (COL/EPI, COL/ADP, and COL/P2Y) showed significant deterioration during ECMO support with rapid restoration after ECMO cessation (p < 0.05), suggesting an ECMO-induced primary hemostasis disorder. A significant increase of vWF antigen after ECMO cessation (p < 0.05) was found with an increase of RCo and CB levels, although it was not significant (p > 0.05).

CONCLUSIONS

Short-term ECMO support induces primary hemostasis pathology. It occurs immediately after initiation but is rapidly restored after ECMO cessation, which is detectable by PFA-200. Despite there being persistent platelet dysfunction after ECMO cessation, as seen with the ROTEM platelet results, the increased levels of vWF antigen might explain the normal results of primary hemostasis detected by PFA-200.

Heyde Syndrome Unveiled: A Case Report with Current Literature Review and Molecular Insights

Heyde syndrome, marked by aortic stenosis, gastrointestinal bleeding from angiodysplasia, and acquired von Willebrand syndrome, is often underreported. Shear stress from a narrowed aortic valve degrades von Willebrand factor multimers, leading to angiodysplasia formation and von Willebrand factor deficiency. This case report aims to raise clinician awareness of Heyde syndrome, its complexity, and the need for a multidisciplinary approach. We present a 75-year-old man with aortic stenosis, gastrointestinal bleeding from angiodysplasia, and acquired von Willebrand syndrome type 2A. The patient was successfully treated with argon plasma coagulation and blood transfusions. He declined further treatment for aortic stenosis but was in good overall health with improved laboratory results during follow-up. Additionally, we provide a comprehensive review of the molecular mechanisms involved in the development of this syndrome, discuss current diagnostic and treatment approaches, and offer future perspectives for further research on this topic.

Difference in activated partial thromboplastin time values with two different reagents according to C-reactive protein values

BACKGROUND

Activated partial thromboplastin time (APTT) is susceptible to reagent composition. This study aimed to investigate a large number of specimens and determine the cause of discrepancies.

METHOD

This study included 18,994 subjects who underwent coagulation tests at our hospital from May 2020 to December 2020. Measuring reagents included HemosIL SynthASil APTT (APTT-SS, Instrumentation Laboratory) and Coagpia APTT-N (APTT-N, Sekisui Medical).

RESULTS

A total of 451 patients demonstrated APTT-N of >39 seconds and an APTT-N/SS ratio of >1.3. A C-reactive protein (CRP) level of ≥1.4 mg/L demonstrated a significant positive correlation, with a higher APTT-N/SS indicating higher CRP levels. All 28 subjects receiving no anticoagulants and who had remaining specimens underwent a cross-mixing test (CMT). Of them, 17 were suspected for lupus anticoagulant (LA) by both the waveform shape and the index of circulating anticoagulant (ICA) value, 6 by the ICA value, and 5 were difficult to determine.

CONCLUSION

This study revealed that the APTT-N prolongation correlated with CRP degree and the transient involvement of LA in CMT results due to CRP. This study indicated various reactivities depending on the assay reagents used. Further testing is warranted if LA is suspected, considering the patient's background.

Factor VIII stimulants and other novel therapies for the treatment of von Willebrand disease: what's new on the horizon?

INTRODUCTION

Von Willebrand disease (VWD) is the most common inherited bleeding disorder, affecting about 0.6% to 1.3% of the population, and is characterized primarily by mucocutaneous bleeding secondary to defective platelet adhesion and aggregation. Current therapeutic options for those with severe disease are limited and require frequent intravenous infusions.

AREAS COVERED

This review discusses the current and recently completed clinical trials involving pathways to FVIII augmentation for the treatment of VWD. Clinical trials registered on clinicaltrials.gov and published data via PubMed searches through June 2024 were included.

EXPERT OPINION

Available treatment options to those with VWD are limited in part due to limited clinical trials, the complexity of VWD types, and the pharmacokinetics of current treatment options. The development of therapeutic options that reduce treatment burden is necessary to improve quality of life and reduce bleeding complications and in recent years there has been an increased interest from industry to apply novel therapeutics for VWD. The FVIII mimetic, emicizumab, has demonstrated early success in patients with severe VWD and is a promising treatment option for those who require prophylaxis. Furthermore, products like efanesoctocog alfa (Altuviiio®) and BT200 have achieved enhanced VWF/FVIII half-life extension could expand the current treatment landscape while concurrently minimizing treatment burden.

Clinical, economic, and health-related quality of life burden associated with von Willebrand disease in adults and children: Systematic and targeted literature reviews

INTRODUCTION

Debilitating clinical complications in von Willebrand disease (VWD) can affect health-related quality of life (HRQoL), increase healthcare costs and cause long-lasting consequences. However, the magnitude of these burdens needs to be more fully explored.

AIM

To estimate the prevalence and burden of clinical complications, the impact on HRQoL and the economic burden associated with VWD.

METHODS

Embase^® , MEDLINE^® , the Cochrane Library and conference proceedings were searched for studies on VWD evaluating clinical complications, HRQoL and cost and resource use.

RESULTS

Among 16 studies assessing clinical complications in VWD, the most prevalent bleeding symptoms were menorrhagia (2%-95% [n = 7 studies]), epistaxis (12%-80% [n = 6]) and easy bruising (46%-65% [n = 2]). Among 17 studies evaluating HRQoL, the most common assessment scales were the generic SF-36 (n = 8 studies) and the EQ-5D (n = 2). Bleeding symptoms were associated with reduced QoL in six of seven studies, and of six studies evaluating treatment impact, four reported improvements in one or more HRQoL components. Among 25 studies on cost and resource use, key observations included higher post-surgery healthcare costs in VWD versus non-VWD patients (n = 1 study) and higher costs and resource use in VWD patients with bleeding complications versus those without (n = 1).

CONCLUSION

Although limited, available evidence suggests that VWD patients experience a high burden of clinical complications, reduced QoL and high healthcare costs. Haemarthrosis is more common in severe VWD than is often assumed, and bleeds (including haemarthrosis) can reduce QoL. Research efforts to improve QoL and other outcomes should be prioritized.

Von Willebrand Disease in Older Patients: A Retrospective Electronic Health Record Review

Von Willebrand disease (VWD) is often diagnosed as a consequence of symptoms experienced with hemostatic stressors, such as menstruation and childbirth. Thus, patients seeking medical care for VWD are generally younger. As a result, the natural course of VWD in older adults has not been well described. A retrospective electronic health record review was performed to provide a descriptive analysis of older VWD patients with at least one clinic visit at the Hemophilia Center of Western Pennsylvania (HCWP) between June 1, 2015, and May 31, 2021, and age 45 or older at the time of the visit. Data collected included VWD-related information, multimorbidity, and medications. Age-related change in von Willebrand factor (VWF) levels and the influence of multimorbidity on VWF levels were assessed. Seventy patients had 131 HCWP clinic visits. Hypertension, 34.3%, and osteoarthritis, 32.3%, were the most common multimorbidity-associated conditions. More than 33% of patients were receiving at least one antihemostatic medication. The most common bleeding symptom was ecchymosis, 22.9%. VWF antigen levels, 0.76 IU/mL, and the proportion of patients with normal VWF levels, 54.5%, increased with age to 0.99 IU/mL, p < 0.001, and 78.8%, p < 0.001, respectively. Multimorbidity did not predict change in VWF levels, p = 0.84. Of 62 invasive procedures performed, bleeding occurred in one of nine where VWD-specific therapy was omitted. These findings underscore the importance of describing the natural course of VWD in older adults, especially the critical nature of determining bleeding risk to guide clinical decision-making with the use of antihemostatic drugs and periprocedural VWD-specific therapy.

Diagnostic Testing for von Willebrand Disease: Trends and Insights from North American Laboratories over the Last Decade

Accurate diagnosis of von Willebrand disease (VWD) depends on the quality, precision, and variability of the laboratory assays. The North American Specialized Coagulation Laboratory Association (NASCOLA) is a provider of external quality assessment (EQA) for approximately 60 specialized coagulation laboratories in North America. In this report, NASCOLA EQA data from 2010 to 2021 are reviewed for trends in methodology and precision among various assays. In particular, recent ASH ISTH NHF WFH (American Society of Hematology, International Society on Thrombosis and Haemostasis, National Hemophilia Foundation, and World Hemophilia Federation) guidelines for diagnosis of VWD are reviewed in light of EQA data. In contrast to other geographic regions, laboratories in North America predominantly use three-assay screening panels (antigen, platelet-binding activity, and factor VIII [FVIII] activity) rather than four-assay panels (antigen, platelet-binding activity, FVIII activity, and collagen-binding activity). They also use latex immunoassays rather than chemiluminescence immunoassays, and the classic ristocetin cofactor (VWF:RCo) assay and monoclonal antibody (VWF:Ab) assay to assess VWF platelet-binding activity over newer recommended assays (VWF:GPIbM and VWF:GPIbR). Factors that may be influencing these North American practice patterns include lack of Food and Drug Administration approval of the VWF:GPIbM, VWF:GPIbR, collagen binding assays, and chemiluminescence methodologies, and the influence of the 2008 National Heart, Lung, and Blood Institute guidelines on laboratory practice. Lastly, systems-based solutions are urgently needed to improve the overall accuracy of laboratory testing for VWD by minimizing preanalytical variables and adopting assay standardization.

Phenotypic and genetic characterizations of the Milan cohort of von Willebrand disease type 2

von Willebrand disease (VWD) type 2 is caused by qualitative abnormalities of von Willebrand factor (VWF). This study aimed to determine the genotypic and phenotypic characterizations of a large VWD type 2 cohort from Milan. We included 321 patients (54% female) within 148 unrelated families from 1995 to 2021. Patients were fully characterized using laboratory phenotypic tests, and the genotypic diagnosis was confirmed by target genetic analysis using Sanger sequencing. Patients were diagnosed with type 2A (n = 98; 48 families), 2B (n = 85; 38 families), 2M (n = 112; 50 families), or 2N (n = 26; 12 families). Eighty-two unique VWF variants, including 8 novel variants, were found. The potential pathogenic effect of novel variants was assessed by in silico analysis. Most patients were heterozygous for a single variant (n = 259; 81%), whereas 37 cases (11%) had 2 variants (4 homozygous, 9 in trans, and 24 in cis). Twenty-five patients (8%) had ≥3 variants, mainly as a result of gene conversions. Among the 82 distinct variants identified, 5 different types, including missense (n = 64), gene conversion (n = 10), synonymous (n = 1), deletion (n = 4), and splice (n = 3), were observed. The results from this large cohort showed that VWD type 2 is invariably due to variants that do not prevent the synthesis of the protein, and a vast majority of patients (88%) had missense variants. Given the complexity of type 2 diagnosis and the necessity of performing several phenotypic tests, genetic analysis for patients suspected of having type 2 is beneficial to establish the correct diagnosis.

Establishing reference intervals for von Willebrand factor multimers

Background

von Willebrand factor (VWF) multimers (VWF:MM) methodologies are technically difficult, laborious, time consuming, non-standardized and results vary between laboratories. A new semi automated VWF:MM assay is available for routine use (Sebia). Due to lack of reference values for VWF:MM fractions, results interpretation can be challenging in some cases. The aim of this study was to determine reference intervals for low molecular weight (LMWM), intermediate molecular weight (IMWM) and high molecular weight (HMWM) multimers.

Methods

By the international cooperation initiated between 4 countries (Estonia, Latvia, France, and USA) 131 samples of relatively healthy individuals were analyzed for VWF:MM (in total 51 males and 80 non-pregnant females aged 17-69 years). Reference intervals were calculated according to CLSI C28-A3 standard.

Results

The proposed reference intervals for VWF:MM were calculated for LMWM 10.4-22.5%, IMWM 22.6-37.6%, HMWM 45.6-66.6%. Age related differences were seen in IMWM and HMWM (p<0.001 and 0.038). There was no gender related difference observed. Geographically LMWM results of France were different from the other regions (p<0.05).

Conclusions

Quantification of VWF:MM fractions, in addition to qualitative assessment of VWF:MM patterns, has the potential to aid in differential diagnosis of von Willebrand disease (VWD) subtypes. The reference values calculated in this study can be used in future research to establish clinical decision limits.

Extracorporeal membrane oxygenation seems to induce impairment of primary hemostasis pathology as measured by a Multiplate analyzer: An observational retrospective study

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) support is often associated with bleeding complications caused by secondary or primary hemostasis pathology. However, there are limited data investigating primary hemostasis using Multiplate aggregometry with specific diagnostics tests for vWF (von Willebrand factor) deficiency.

AIMS

The aim of this study was to find out whether short-term ECMO produces the pathology of primary hemostasis that is detected by Multiplate aggregometry and to investigate the pathology of vWF.

METHODS

In this study, blood samples of 20 patients undergoing lung transplantations with short-term perioperative ECMO support were analyzed. The multimeric structure, the levels of von Willebrand factor antigen (vWF), ristocetin cofactor (RCo), collagen-binding protein (CB), and the results of multiple electrode aggregometry RISTO (ristocetin), ADP (adenosine diphosphate), ASPI (Aspirin®; arachidonic acid), and TRAP (thrombin receptor activating peptide) tests were compared to the samples obtained before and after ECMO support.

RESULTS

The Multiplate ADP and RISTO tests showed the presence of significant pathology in primary hemostasis after surgery (p < 0.05), suggesting the presence of acquired platelet dysfunction. Although the RISTO tests suggest the presence of acquired vWF deficiency, laboratory tests for vWF antigen and RCo and CB tests showed an increase in this case. The multimeric structure of vWF did not show clinically significant deterioration.

CONCLUSIONS

Multiple aggregometry ADP, ASPI, and TRAP tests seem to be able to detect primary hemostasis pathology (platelets aggregation and adhesion pathology) that is present during short-term perioperative ECMO support in lung transplantation procedures. Interestingly, RISTO tests seem to be more suitable for the diagnosis of platelet dysfunction than the diagnosis of acquired vWF deficiency in this situation.

The Intriguing Relationships of von Willebrand Factor, ADAMTS13 and Cardiac Disease

von Willebrand factor (VWF) is an adhesive protein involved in primary hemostasis and facilitates platelet adhesion to sites of vascular injury, thereby promoting thrombus formation. VWF exists in plasma as multimers of increasing size, with the largest (high molecular weight; HMW) expressing the greatest functional activity. A deficiency of VWF is associated with a bleeding disorder called von Willebrand disease (VWD), whereas an excess of VWF, in particular the HMW forms, is associated with thrombosis. ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif-13), also known as VWF-cleaving protease, functions to moderate the activity of VWF by cleaving multimers of VWF and limiting the expression of the largest multimers of VWF. A deficiency of ADAMTS13 is therefore associated with an excess of (HMW forms of) VWF, and thus thrombosis. Indeed, any disturbance of the VWF/ADAMTS13 ratio or ‘axis’ may be associated with pathophysiological processes, including prothrombotic tendency. However, both thrombosis or bleeding may be associated with such disturbances, depending on the presenting events. This review evaluates the relationship of VWF and ADAMTS13 with cardiac disease, including cardiac failure, and associated pathophysiology.

Diagnosis of von Willebrand disease: An assessment of the quality of testing in North American laboratories

BACKGROUND

Laboratory diagnosis of von Willebrand Disease (VWD) is complex. Reliance on laboratory testing can be problematic as different VWD screening panels, assays and methodologies can produce analytic variability in test results.

OBJECTIVES

To compare the degree of imprecision among the VWD assays and within the platelet binding activity (PBA) assays, to determine the consensus among the VWD assays for correct classification of sample results, and to determine consensus among laboratories' von Willebrand factor (VWF) multimer interpretations and final interpretations of the VWD panels.

PATIENTS/METHODS

Proficiency testing results from the North American Specialized Coagulation Laboratory Association (NASCOLA) submitted by laboratories from 2010 to 2019 for all normal, type (T) 1 VWD and T2 VWD samples were analysed.

RESULTS AND CONCLUSIONS

Imprecision was lowest for VWF antigen and highest for collagen binding activity (CBA) with median coefficient of variation (CV) of 12% (interquartile range (IQR) 7%) and 23% (IQR 21%) respectively. Within the VWF PBA assays, the gain-of-function mutant GP1b binding (VWF: GP1bM) methods had the least imprecision (CV 9%, IQR 10%). All assays, including the various PBA methods had excellent consensus. The majority of laboratories agreed that normal (median consensus-82%, IQR 16%) and T1 VWD (median consensus-100%, IQR 9%) samples had normal multimer distribution. Consensus among laboratories for final interpretations was excellent for normal samples (median 81%, IQR 8%), good for T1 VWD samples (median 59%, IQR 9%), and fair for T2 VWD samples (median 44%, IQR 21%). Consensus on final interpretation decreased as sample complexity increased.

Why is Misdiagnosis of von Willebrand Disease Still Prevalent and How Can We Overcome It? A Focus on Clinical Considerations and Recommendations

Despite von Willebrand disease (VWD) being the most common inherited bleeding disorder, its accurate diagnosis is frequently shrouded by diagnostic pitfalls. VWD is frequently under-diagnosed, over-diagnosed and misdiagnosed, leading to significant avoidable patient morbidity and health care system burden. At the heart of this dilemma lies the heterogeneity and complexity of von Willebrand factor (VWF) and associated defects, and the necessity of coalescing clinical and laboratory features to obtain an accurate diagnosis. Common pitfalls include poor clinical and scientific understanding and familiarity with VWD, incomplete clinical history and lack of routine use of standardised bleeding assessment tools (BAT), difficulty in accessing a comprehensive repertoire of laboratory tests, significant pre-analytical, analytical and post-analytical issues, and lack of expertise in laboratory testing and interpretation. Errors, resulting in under-diagnosis, over-diagnosis, and misdiagnosis of VWD, are presented and discussed. Strategies to minimise errors include better education of clinicians and laboratory staff on VWD, routine use of validated BAT, utilising a comprehensive gamut of laboratory investigations according to a standardised algorithm, and repeating testing to minimise pre-analytical errors. Recommendations on appropriate patient selection for VWD testing, how VWD should be investigated in the laboratory, and how to ensure test results are accurately interpreted in the correct clinical context are detailed.

ASH ISTH NHF WFH 2021 guidelines on the diagnosis of von Willebrand disease

BACKGROUND

von Willebrand disease (VWD) is the most common inherited bleeding disorder known in humans. Accurate and timely diagnosis presents numerous challenges.

OBJECTIVE

These evidence-based guidelines of the American Society of Hematology (ASH), the International Society on Thrombosis and Haemostasis (ISTH), the National Hemophilia Foundation (NHF), and the World Federation of Hemophilia (WFH) are intended to support patients, clinicians, and other health care professionals in their decisions about VWD diagnosis.

METHODS

ASH, ISTH, NHF, and WFH established a multidisciplinary guideline panel that included 4 patient representatives and was balanced to minimize potential bias from conflicts of interest. The Outcomes and Implementation Research Unit at the University of Kansas Medical Center (KUMC) supported the guideline-development process, including performing or updating systematic evidence reviews up to 8 January 2020. The panel prioritized clinical questions and outcomes according to their importance for clinicians and patients. The panel used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach, including GRADE Evidence-to-Decision frameworks, to assess evidence and make recommendations, which were subsequently subject to public comment.

RESULTS

The panel agreed on 11 recommendations.

CONCLUSIONS

Key recommendations of these guidelines include the role of bleeding-assessment tools in the assessment of patients suspected of VWD, diagnostic assays and laboratory cutoffs for type 1 and type 2 VWD, how to approach a type 1 VWD patient with normalized levels over time, and the role of genetic testing vs phenotypic assays for types 2B and 2N. Future critical research priorities are also identified.

Obstacles to Early Diagnosis and Treatment of Inherited von Willebrand Disease: Current Perspectives

Von Willebrand disease (VWD), the most common inherited bleeding disorder, is highly heterogeneous, and its early diagnosis may be difficult, especially for mild cases and in qualitative von Willebrand factor (VWF) defects. Appropriate VWD diagnosis requires the combination of personal and/or family history of bleeding and abnormal VWF laboratory testing. The use of bleeding assessment tools has been helpful in standardizing bleeding history collection and quantification of bleeding symptoms to select patients who may benefit of further hemostatic testing. Type 1 and 3 VWD which represent quantitative VWD variants are relatively easy to diagnose. The diagnosis of type 2 VWD requires multiple assessments to evaluate the effects induced by the responsible abnormality on the heterogeneous functions of VWF. Sensitive and reproducible tests are needed to evaluate different VWF activities, starting from measuring VWF-platelet interaction. In the recent years, several increasingly sensitive, rapid and automated assays have been developed, but they are not widely available so far. Genetic testing for VWD diagnosis is not a common practice because VWF gene is very large and highly polymorphic and therefore it is used only in specific cases. It is evident that the early and correct VWD diagnosis allows optimal management of bleeding and situations at risk. Tranexamic acid, desmopressin, replacement therapy with plasma-derived concentrates with a variable content of VWF and FVIII, or the new recombinant VWF are the different therapeutic options available. Careful VWD classification guides treatment because desmopressin is widely used in type 1 while replacement therapy is the cornerstone of treatment for type 2 and 3 variants.

Anticoagulant treatment and bleeding complications in patients with left ventricular assist devices

INTRODUCTION

The treatment options for advanced heart failure patients drastically changed with the introduction of left ventricular assist devices (LVADs), either as bridge to transplant or as destination therapy for patients ineligible for transplant. Despite major benefits in terms of survival, functional status and quality of life, managing patients with LVADs comes with several challenges. The most significant challenge is balancing between the risks of thrombotic and bleeding complications.

AREAS COVERED

The present review describes the pathophysiological mechanisms explaining the alterations in the hemostatic profile of LVAD patients, and summarizes current evidence to guide clinical decision making with regard to anticoagulant treatment and management of bleeding complications.

EXPERT OPINION

LVAD patients require life-long anticoagulant therapy to reduce the risk of pump thrombosis. However, exposing LVAD patients to anticoagulant therapy, in combination with common acquired coagulopathies after LVAD implantation such as acquired von Willebrand syndrome, comes with high risks of bleeding. There is a need for randomized controlled trials in LVAD patients to determine the optimal antithrombotic regimen and find the most effective balance between thrombotic and bleeding complications. In addition, strategies to specifically target the acquired von Willebrand syndrome and its associated angiodysplasias need to be evaluated in the LVAD population.

Potential Undiagnosed VWD Or Other Mucocutaneous Bleeding Disorder Cases Estimated From Private Medical Insurance Claims

Introduction

Von Willebrand disease (VWD) is a common inherited bleeding disorder, but awareness among health care professionals is low. We estimated the number of cases of undiagnosed VWD or other mucocutaneous bleeding disorders among commercially insured patients in the United States with a recent history of bleeding events.

Methods

Patients with a VWD diagnosis who were users of or candidates for von Willebrand factor replacement were identified from the IMS PharMetrics Plus Database (2006–2015). We constructed a unary patient-finding model based on 12 prediagnosis variables that best defined this population, and applied this to undiagnosed patients with recent bleeding events from the same database. Cases of symptomatic undiagnosed VWD or other mucocutaneous bleeding disorders in the commercially insured population were estimated from the “best fit” (positive predictive value [PPV] 83%) and “good fit” (PPV 75%) patients thus identified.

Results

Overall, 507,668 undiagnosed patients with recent bleeding events were identified (86% female, 14% male). Application of the VWD model identified 3318 best-fit and 37,163 good-fit patients; 91% of best-fit patients were females aged <46 years, with heavy menstrual bleeding as the most common claim. Projection to the full commercially insured US population suggested that 35,000–387,000 patients may have symptomatic, undiagnosed VWD or other mucocutaneous bleeding disorders.

Discussion

Computer modeling suggests there may be a significant number of patients with symptomatic, undiagnosed VWD or other mucocutaneous bleeding disorder in the commercially insured population. Enhanced awareness of VWD symptoms and their impact, and of screening and testing procedures, may improve the diagnosis of VWD and reduce disease burden.

Updated overview on von Willebrand disease: focus on the interest of genotyping

Introduction: Von Willebrand disease (VWD) is the most common inherited bleeding disorder, characterized by a quantitative or qualitative defect of von Willebrand factor (VWF), a multimeric glycoprotein crucial for primary hemostasis and coagulation. VWD pathophysiology is heterogeneous as it includes several types and subtypes which therapeutic management is different. The mainstays of VWD treatment are desmopressin and replacement therapy based on both plasma-derived concentrates and a recently developed recombinant VWF. VWD definitive diagnosis is achieved by a battery of phenotypic biologic assays and genotyping is currently performed mostly for research.Areas covered: This narrative review will firstly present a general overview on VWD epidemiology, pathophysiology, classification, clinics, phenotypic biologic diagnosis, and treatment. Secondly, a focus on VWD genotyping will be presented with specific emphasis on the evolution of its technical aspects, its applications for research dedicated to a better understanding of VWD pathophysiology and epidemiology and its interest in both a faster diagnosis and an optimal treatment of VWD.Expert opinion: Based on analysis of the literature, it can be concluded that the fast evolution of genetic techniques together with the development of innovating treatments may significantly change diagnostic flow charts for VWD and their use for specific and personalized treatment.

How I manage severe von Willebrand disease

Von Willebrand disease (VWD) is the most common inherited bleeding disorder. Most patients with mild and moderate VWD can be treated effectively with desmopressin. The management of severe VWD patients, mostly affected by type 2 and type 3 disease, can be challenging. In this article we review the current diagnosis and treatment of severe VWD patients. We will also discuss the management of severe VWD patients in specific situations, such as pregnancy, delivery, patients developing alloantibodies against von Willebrand factor and VWD patients with recurrent gastrointestinal bleeding. Moreover, we review emerging treatments that may be applied in future management of patients with severe VWD.

Automated assays for von Willebrand factor activity

von Willebrand factor (VWF) ristocetin cofactor activity (VWF:RCo) by platelet aggregometry has been considered the gold standard for evaluating the ability of VWF to bind platelets for over 40 years. Many automated systems no longer require platelets and rather rely on agglutination of latex particles. Automated methods of measuring VWF activity have improved performance characteristics and are performed on the same coagulation instruments used for routine testing via immunoturbidimetric methodology. Alternatively, a newer chemiluminescence assay system for measuring VWF activity demonstrates excellent performance characteristics. As these methods are becoming widely used, it is important to assess their performance in diagnosing and monitoring different types of von Willebrand disease. We review the automated methodologies and the published performance of these VWF assays. Advantages and limitations of these automated methods are discussed.

The impact of rivaroxaban on primary hemostasis in patients with venous thrombosis

Factor Xa inhibitors are safe and effective alternatives to warfarin, but several studies indicate that rivaroxaban may cause a different risk profile for bleeding. For instance, while the risk of major bleeding in general may be lower with rivaroxaban than for warfarin, the risk of gastrointestinal bleeding or abnormal uterine bleeding may be higher. The underlying mechanisms for these differences are not known, and the effect of rivaroxaban on primary hemostasis is poorly understood. The aim of this study was to investigate the effect of rivaroxaban on platelet function, P-selectin and von Willebrand factor (VWF) antigen and activity. Patients with venous thrombosis assigned to 3 months of treatment due to temporary risk factors were included. Blood was collected both during (on-treatment) and 4-6 weeks after end of treatment (without treatment). The platelet reactivity was assessed by light transmission aggregometry. P-selectin was measured by an enzyme-linked immunosorbent assay and vWF antigen and activity by latex immunoagglutination assays. Platelet reactivity during on-treatment (trough- and peak concentration) was similar to values without treatment. There was a trend toward a reduction of P-selectin during rivaroxaban treatment (peak concentration) compared to value without treatment (p = 0.06). There were no differences in vWF antigen and activity between the different time-points. We found no difference in platelet reactivity or vWF antigen/activity during rivaroxaban treatment compared with values without treatment. Apart from possibly causing a reduction of P-selectin, rivaroxaban seems not to influence primary hemostasis.

Combination of acquired von Willebrand syndrome (AVWS) and Glanzmann thrombasthenia in monoclonal gammopathy of uncertain significance (MGUS), a case report

Background

Autoimmune paraphenomena, are associated with B-cell lymphoproliferative disorders, including monoclonal gammopathy of uncertain significance. These paraphenomena can rarely include acquired bleeding disorders.

Case presentation

This case study reports an unusual clinical presentation of 2 acquired bleeding disorders, Acquired von Willebrand syndrome (disease) and Acquired Glanzmann's thrombasthenia, in an elderly patient with monoclonal gammopathy of uncertain significance.

Conclusions

Acquired bleeding disorders are often underdiagnosed and a high degree of clinical suspicion is required. The patient in this study demonstrated platelet aggregometry which was atypical for isolated Glanzmann's thrombosthenia because of the severe concomitant endogenous decrease in von Willebrand factor. There was an absence of platelet aggregation to all tested agonists including ristocetin. Once the diagnosis was made, however, the patient showed a partial response to intravenous immunoglobulin confirming the immunological pathogenesis in this case. This case highlights the need to consider acquired bleeding disorders in patients with a possible predisposing factor.

Clinically relevant differences between assays for von Willebrand factor activity

Essentials It is unclear whether there are differences between von Willebrand factor (VWF) activity assays. We compared the four most used VWF activity assays in 661 von Willebrand disease (VWD) patients. All assays correlated excellently, but a discrepant classification was seen in 20% of patients. Differences between VWF activity assays have a large impact on the classification of VWD. SUMMARY: Background Measuring the ability of von Willebrand factor (VWF) to bind to platelets is crucial for the diagnosis and classification of von Willebrand disease (VWD). Several assays that measure this VWF activity using different principles are available, but the clinical relevance of different assay principles is unclear. Objective To compare the four most widely used VWF activity assays in a large VWD patient population. Methods We measured VWF:RCo (ristocetin to activate VWF + whole platelets), VWF:GPIbR (ristocetin + platelet glycoprotein Ib receptor [GPIb] fragments), VWF:GPIbM (gain-of-function GPIb fragments that bind VWF spontaneously without ristocetin) and VWF:Ab (monoclonal antibody directed against the GPIb binding epitope of VWF to mimic platelets) in 661 VWD patients from the nationwide 'Willebrand in the Netherlands' (WiN) Study. Results All assays correlated excellently (Pearson r > 0.9), but discrepant results led to a different classification for up to one-fifth of VWD patients. VWF:RCo was not sensitive enough to classify 18% of patients and misclassified half of genotypic 2B VWD patients, especially those with p.Arg1306Trp. VWF:GPIbR was more sensitive, accurately classified the vast majority of patients, and was unaffected by the p.Asp1472His variant that causes artificially low VWF:RCo. VWF:GPIbM was the most precise assay but misclassified over a quarter of genotypic 2A, 2B and 3 patients. VWF:Ab, often not considered an actual VWF activity assay, performed at least equally to the other assays with regard to accurate VWD classification. Conclusion Although the different VWF activity assays are often considered similar, differences between assays have a large impact on the classification of VWD.

Preoperative screening for bleeding disorders: A comprehensive laboratory assessment of clinical practice

BACKGROUND

Patients with mild bleeding disorders are at risk of perioperative bleeding, but screening for these disorders remains challenging.

OBJECTIVES

We aimed to assess the prevalence of hemostatic abnormalities in patients with and without reported bleeding symptoms on a preoperative questionnaire, consisting of guideline-proposed questions, and appraised the diagnostic value of several screening modalities for the identification of patients with hemostatic abnormalities.

METHODS

In this observational study, 240 patients with and 95 patients without bleeding symptoms on the preoperative questionnaire were included. Patients with known bleeding disorders, antithrombotic drugs, thrombocytopenia, and anemia were excluded. Preoperatively, all patients underwent elaborate hemostatic testing. Hemostatic abnormalities were defined as coagulation, vWF, or fibrinolysis factor levels below reference range and platelet function defects. Screening modalities included the ISTH Bleeding Assessment Tool (ISTH-BAT), PT, aPTT, TT, Euglobulin Lysis Time (ELT), and Platelet Function Analyser (PFA).

RESULTS

In 21 of 240 (8.8%) patients reporting bleeding symptoms, hemostatic abnormalities were found, including 7 reduced coagulation factor levels, 10 platelet function abnormalities, and 4 reduced vWF levels. In comparison, 10 of 95 (10.5%) patients not reporting bleeding symptoms had abnormalities. The ISTH-BAT could not identify patients with abnormalities, while PT, aPTT, TT, ELT, and PFA had high specificity but low sensitivity to detect abnormalities.

CONCLUSIONS

The prevalence of hemostatic abnormalities in both patients with and without reported bleeding symptoms was 9%-10%. This suggests that the guideline-based questionnaire cannot differentiate between patients with and without abnormalities, while the discriminative power of the screening modalities is also limited.

A comparative analysis of different automated von Willebrand factor glycoprotein Ib-binding activity assays in well typed von Willebrand disease patients

Essentials Von Willebrand ristocetin cofactor activity (VWF:RCo) is not a completely reliable assay. Three automated VWF activity assays were compared within a von Willebrand disease (VWD) cohort. Raw values for all three assays were virtually the same. An overall problem within type 2A/IIE VWD using VWF:GPIb-binding activity/VWF:Ag was observed.

SUMMARY

Background von Willebrand disease (VWD) is an inherited bleeding disorder caused by quantitative (type 1 and 3) or qualitative (type 2) von Willebrand factor (VWF) defect. VWD diagnosis and classification require numerous laboratory tests. VWF: glycoprotein Ib (GPIb)-binding activity assays are used to distinguish type 1 from type 2 VWD. Objectives Three different automated VWF:GPIb-binding activity assays were compared. Patients and methods BC-VWF:RCo (Siemens Healthcare Diagnostics), HemosIL® VWF:RCo (Instrumentation Laboratory) and INNOVANCE® VWF:Ac (Siemens Healthcare Diagnostics) were performed in a well typed VWD cohort (n = 142). Results Based on the three most used VWD parameters (FVIII:C, VWF:Ag and VWF:GPIb-binding activity) and using a cut-off of <0.70 for type 2 VWD revealed sensitivity and specificity of, respectively, 92% and 72.4% for VWF:RCo/VWF:Ag, 84% and 89.7% for VWF:GPIbR/VWF:Ag, and 92% and 85.1% for VWF:GPIbM/VWF:Ag, whereas a lowered cut-off of < 0.60 resulted in reduced sensitivity with increased specificity for all assays. Conclusion VWD classification based on FVIII:C, VWF:Ag and VWF:GPIb-binding activity revealed an overall problem with normal VWF:GPIb-binding activity/VWF:Ag within type 2, especially type 2A/IIE. Although all assays were practically identical, BC-VWF:RCo had higher %CV compared with both new assays but comparable lower limit of quantification (LLOQ) ~4 IU dL-1 . No clear improved distinction between type 1 and 2 VWD with new assays was seen.

BC-VWF

RCo and HemosIL® are ristocetin dependent, whereas INNOVANCE® does not rely upon ristocetin and is not influenced by VWF polymorphisms increasing VWF:GPIb-binding activity levels. INNOVANCE® seems to be the best choice as a first-line VWF:GPIb-binding activity assay, providing the best balance between sensitivity and specificity for type 2 VWD.

Role of multimeric analysis of von Willebrand factor (VWF) in von Willebrand disease (VWD) diagnosis: Lessons from the PCM-EVW-ES Spanish project

The multimeric analysis (MA) of plasma von Willebrand factor (VWF) evaluates structural integrity and helps in the diagnosis of von Willebrand disease (VWD). This assay is a matter of controversy, being considered by some investigators cumbersome and only slightly informative. The centralised study ‘Molecular and Clinical Profile of von Willebrand Disease in Spain (PCM-EVW-ES)’ has been carried out by including the phenotypic assessment and the genetic analysis by next generation sequencing (NGS) of the VWF gene (VWF). The aim of the present study was to evaluate the role of MA to the diagnosis of these patients and their potential discrepancies. Two hundred and seventy out of 480 patients centrally diagnosed with VWD had normal multimers, 168 had abnormal multimers and 42 a total absence of multimers. VWF MA was of great significance in the diagnosis of 83 patients (17.3%), it was also of help in the diagnosis achieved in 365 additional patients (76%) and was not informative in 32 cases (6.7%). With regard to discrepancies, 110 out of 480 (23%) patients centrally diagnosed with VWD presented some kind of discordance between VWF:RCo/VWF:Ag and/or VWF:CB/VWF:Ag ratios, multimeric study and/or genetic results. The VWF MA was key in the presence of novel mutations as well as in cases with phenotypic discrepancies. A comparison between the contribution of MA and VWF:CB showed a clearly higher contribution of the former in the diagnostic process. These data seem to reinforce the relevance of the VWF MA in VWD diagnosis, despite all its limitations.

Preclinical evaluation of a semi-automated and rapid commercial electrophoresis assay for von Willebrand factor multimers

BACKGROUND

The von Willebrand factor (VWF) multimer test is required to correctly subtype qualitative type 2 von Willebrand disease (VWD). The current VWF multimer assays are difficult, nonstandardized, and time-consuming. The purpose of this study was to evaluate the clinical utility of the commercial VWF multimer kit by Sebia (Lisses, France), an electrophoresis technique yielding same-day results.

METHODS

Ten healthy volunteer plasma samples, in-house reference plasma (IRP) and commercial normal plasma (CNP) samples, 10 plasma samples from patients with a known VWD type, 1 hemophilia A plasma sample, and 7 external quality assurance (EQA) samples were analyzed using the commercial VWF multimer kit. Additional coagulation testing included measurements of VWF antigen (VWF:Ag), VWF activity (VWF:Ac), and FVIII activity (FVIII:C).

RESULTS

The CNP results revealed a relative loss of the highest molecular weight multimers; therefore, IRP was preferred as the reference sample. The interpretations of 10 patients with a known VWD type could be successfully reproduced and agreed with previous VWF multimer results. In all EQA surveys, the multimer results and final VWD diagnosis agreed with expert opinion.

CONCLUSIONS

The VWF multimer assay by Sebia is easy to perform and can be successfully implemented in any clinical laboratory for second-stage evaluation of VWD. The resolution power of multimer distribution is adequate to correctly classify VWD types 1, 2A, 2B, and 3.

Genetic Variation in the von Willebrand Factor Gene in Swedish von Willebrand Disease Patients

von Willebrand factor (VWF) level and function are influenced by genetic variation in VWF and several other genes in von Willebrand disease type 1 (VWD1) patients. This study comprehensively screened for VWF variants and investigated the presence of ABO genotypes and common and rare VWF variants in Swedish VWD1 patients. The VWF gene was resequenced using Ion Torrent and Sanger sequencing in 126 index cases historically diagnosed with VWD. Exon 7 of the ABO gene was resequenced using Sanger sequencing. Multiplex ligation-dependent probe amplification analysis was used to investigate for copy number variants. Genotyping of 98 single nucleotide variants allowed allele frequency comparisons with public databases. Seven VWD2 mutations and 36 candidate VWD1 mutations (5 deletions, 4 nonsense, 21 missense, 1 splice, and 5 synonymous mutations) were identified. Nine mutations were found in more than one family and nine VWD1 index cases carried more than one candidate mutation. The T-allele of rs1063857 (c.2385T > C, p.Y795 = ) and blood group O were both frequent findings and contributed to disease in the Swedish VWD1 population. VWD2 mutations were found in 20 and candidate VWD1 mutations in 51 index cases out of 106 (48%). VWF mutations, a VWF haplotype, and blood group O all contributed to explain disease in Swedish VWD1 patients.

How I treat type 2B von Willebrand disease

Type 2B von Willebrand disease (VWD) is an inherited bleeding disorder caused by changes in von Willebrand factor (VWF) that enhance binding of VWF to GPIb on platelets. Although this disorder is seemingly well defined because of this single molecular defect, in reality type 2B VWD is a clinically heterogeneous disorder that can be difficult to identify and manage. Diagnostic criteria include a history of mucocutaneous bleeding, laboratory studies showing enhanced VWF binding of platelets and/or a 2B VWD genetic variant, and a family history consistent with autosomal dominant inheritance. Thrombocytopenia, although not always present, is common and can be exacerbated by physiologic stressors such as pregnancy. The mainstay of therapy for type 2B VWD is VWF replacement therapy. Adjunct therapies useful in other types of VWD, such as antifibrinolytics, are also used in type 2B VWD. 1-Desamino-8-d-arginine vasopressin (DDAVP) is controversial because of exacerbation of thrombocytopenia, but is, in practice, sometimes used for minor bleeding. Here we review the available evidence and provide 3 clinical cases to illustrate the intricacies of diagnosing type 2B VWD to describe the response to DDAVP and to review complexities and management during pregnancy.

Monitoring of coagulation factor therapy in patients with von Willebrand disease type 3 using a microchip flow chamber system

Patients with type 3 von Willebrand disease (VWD-3) have no measurable levels of VW factor (VWF) and usually require treatment with VWF-FVIII concentrate to prevent and/or stop bleeding. Even though the patients are treated prophylactically, they may experience bleeding symptoms. The aim of this study was to evaluate the effect of VWF-FVIII concentrate treatment in VWD-3 patients with the Total Thrombus Analysis System (T-TAS®), which measures thrombus formation under flow conditions. Coagulation profiles of 10 VWD-3 patients were analysed using T-TAS before and 30 minutes after VWF-FVIII concentrate (Haemate®) injection. Results were compared to VWF- and FVIII activity in plasma, and results with thromboelastometry and ris-tocetin-activated platelet impedance aggregometry (Multiplate®) in whole blood. For comparison, 10 healthy controls were also analysed with T-TAS. A median dose of 27 (range 15–35) IU/kg of VWF-FVIII concentrate increased VWF- and FVIII activity as expected. T-TAS thrombus formation was enhanced when a tissue factor/collagen-coated flow chamber was used at low shear, but treatment effects at high shear using a collagen-coated flow chamber were minimal. Whole blood coagulation assessed by thromboelastometry was normal and did not change (p > 0.05) but ristocetin-induced platelet aggregation improved (p < 0.001). In conclusion, T-TAS detects effects of VWF-FVIII concentrate treatment on coagulation-dependent thrombus formation at low shear, but minor effects are observed on platelet-dependent thrombus formation at high shear. The poor prediction of bleeding by conventional laboratory monitoring in VWD-3 patients might be related to insufficient restoration of platelet-dependent thrombus formation.

Von Willebrand disease mutation spectrum and associated mutation mechanisms

Von Willebrand disease (VWD) is a bleeding disorder that is mainly caused by mutations in the multimeric protein von Willebrand factor (VWF). These mutations may lead to deficiencies in plasma VWF or dysfunctional VWF. VWF is a heterogeneous protein and over the past three decades, hundreds of VWF mutations have been identified. In this review we have organized all reported mutations, spanning a timeline from the late eighties until early 2017. This resulted in an overview of 750 unique mutations that are divided over the VWD types 1, 2A, 2B, 2M, 2N and 3. For many of these mutations the disease-causing effects have been characterized in vitro through expression studies, ex vivo by analysis of patient-derived endothelial cells, as well as in animal or (bio)physical models. Here we describe the mechanisms associated with the VWF mutations per VWD type.

Whole blood ristocetin-activated platelet impedance aggregometry (Multiplate) for the rapid detection of Von Willebrand disease

Von Willebrand disease (VWD) is the most common bleeding disorder, but no bedside tests specific for Von Willebrand factor are available. The objective of this study was to evaluate the diagnostic accuracy of whole blood ristocetin-induced platelet aggregometry (WB-RIPA) in VWD. WB-RIPA was performed in VWD patients (n=100) and healthy controls (n=17) using the Multiplate® platelet impedance aggregometry platform. The diagnostic properties of the test were described as sensitivity/specificity, positive and negative predictive value, and ROC area under the curve (AUC). Patients with VWD had impaired platelet aggregation by WB-RIPA. At a cut-off of 98 U, the test sensitivity and specificity of WB-RIPA for VWD was 0.95 and 0.53. A cut-off of 60 U provided a specificity of 1.00 with reduced sensitivity of 0.76. All patients with type 3 VWD and >90 % of patients with type 2 VWD were accurately distinguished from the controls. Incorrect classifications were attributable to patients with type 1 VWD, showing partly overlapping WB-RIPA results with healthy controls. Remarkably, these patients had lower bleeding scores and higher VWF activity than other type 1 VWD patients. Overall, WB-RIPA discriminated VWD patients from healthy controls accurately with a ROC AUC of 0.94. These results show that WB-RIPA is a promising diagnostic test for VWD, especially when timely results are required. Depending on the chosen test threshold, WB-RIPA could be clinically used as a rule out test, or to suggest patients in whom further testing for VWD is warranted.

Development of a novel flow cytometric immunobead array to quantify VWF: Ag and VWF: GPIbR and its application in acute myocardial infarction

OBJECTIVES

Both von Willebrand disease (VWD) and acute myocardial infarction (AMI) involve quantitative and qualitative changes in von Willebrand factor (VWF). Our objective was to develop a rapid and precise flow cytometric immunobead array (FCIA) to quantify VWF antigen (VWF:Ag) and ristocetin-triggered platelet glycoprotein Ib binding (VWF:GPIbR) and apply it in a clinical setting.

METHODS

Microbeads, coated with monoclonal antibodies for SZ29 or SZ151 IgG, were incubated with diluted plasma. VWF-binding microbeads were detected with FITC-conjugated sheep-anti-human VWF IgG by flow cytometry. Plasma VWF:Ag and VWF:GPIbR levels in normal controls (CTL; n=105), patients with VWD (n=21), and patients with AMI (n=146) were tested by FCIA and ELISA in parallel. ADAMTS13 activity and VWF multimer analyses were also implemented.

RESULTS

Our novel FCIA showed a strong correlation with the ELISA results (VWF:Ag, r=.855; VWF:GPIbR, r=.813). The intra-assay coefficient variations (CVs) of VWF:Ag-FCIA and VWF:GPIbR-FCIA were 9.2% and 7.7%, respectively, and the interassay CVs were 12.6% and 13.5%, respectively. Plasma VWF:Ag and VWF:GPIbR levels were significantly higher in patients with AMI than in CTL (P<.0001), whereas the ratios of ADAMTS13/VWF:Ag and ADAMTS13/VWF:GPIbR were significantly lower (P<.0001). Levels of plasma ultra-large VWF (UL-VWF) were dramatically increased in patients with AMI.

CONCLUSIONS

The novel VWF:Ag and VWF:GPIbR-FCIA assays were found to be simpler, more specific, and more accurate than the classical ELISA method. In addition, elevated VWF:GPIbR and UL-VWF may contribute to the pathogenesis of AMI.

Laboratory monitoring of replacement therapy for major surgery in von Willebrand disease

Von Willebrand disease (VWD) is an inherited haemorrhagic disorder caused by a quantitative or qualitative defect of von Willebrand factor (VWF), a multimeric plasma glycoprotein that plays a key role in platelet adhesion to the subendothelium and acts as a carrier of factor VIII (FVIII) in blood. Patients with VWD experience bleeding symptoms that are mainly localized in mucous membranes and soft tissues, and their severity depends on the degree of the primary reduction in VWF and the secondary deficiency of FVIII in plasma. Because VWD patients are also at increased risk of perioperative bleeding, a prophylactic treatment aimed to correct the dual haemostatic defect (i.e. VWF and FVIII) is warranted. This review summarizes knowledge on the current management of patients undergoing major surgery, focusing on the peri-surgical laboratory monitoring of replacement therapy with VWF/FVIII concentrates. We suggest to monitor plasma levels of FVIII coagulant activity in the postoperative period rather than a surrogate maker of platelet-binding VWF activity as the ristocetin cofactor assay and its recent modifications.

Laboratory Testing for von Willebrand Factor Activity by Glycoprotein Ib Binding Assays (VWF:GPIb)

In addition to assessment of von Willebrand factor (VWF) antigen (VWF:Ag), the first-line laboratory investigation of possible von Willebrand disease (VWD) often includes an assay to measure GPIb (glycoprotein Ib) binding activity of VWF. A decreased GPIb binding activity is characteristic for most of the VWD types. For many years, the most frequently used assay for measuring GPIb binding activity was the ristocetin cofactor assay (VWF:RCo), which measures the agglutination of fixed human platelets by VWF in the presence of ristocetin. Because of performance issues, including high assay variability and a lack of VWF sensitivity, this assay is currently being replaced or supplemented by assays based on the binding of VWF to recombinant GPIb. One published method (now abbreviated VWF:GPIbR) uses wild-type GPIb for triggering the binding reaction in the presence of ristocetin. Another more widely used method (now abbreviated VWF:GPIbM) uses gain-of-function GPIb without ristocetin; this permits spontaneous binding of VWF to GPIb and avoids problems associated with the nonphysiological substance ristocetin. The binding of VWF to GPIb can be quantified by using different principles, e.g., ELISA, particle agglutination, or chemiluminescence. The following chapter describes a ristocetin-free method based on particle agglutination in more detail.

A microfluidic model of hemostasis sensitive to platelet function and coagulation

Hemostasis is the process of sealing a vascular injury with a thrombus to arrest bleeding. The type of thrombus that forms depends on the nature of the injury and hemodynamics. There are many models of intravascular thrombus formation whereby blood is exposed to prothrombotic molecules on a solid substrate. However, there are few models of extravascular thrombus formation whereby blood escapes into the extravascular space through a hole in the vessel wall. Here, we describe a microfluidic model of hemostasis that includes vascular, vessel wall, and extravascular compartments. Type I collagen and tissue factor, which support platelet adhesion and initiate coagulation, respectively, were adsorbed to the wall of the injury channel and act synergistically to yield a stable thrombus that stops blood loss into the extravascular compartment in ~7.5 min. Inhibiting factor VIII to mimic hemophilia A results in an unstable thrombus that was unable to close the injury. Treatment with a P2Y12 antagonist to reduce platelet activation prolonged the closure time two-fold compared to controls. Taken together, these data demonstrate a hemostatic model that is sensitive to both coagulation and platelet function and can be used to study coagulopathies and platelet dysfunction that result in excessive blood loss.

A diagnostic approach to mild bleeding disorders

Mild inherited bleeding disorders are relatively common in the general population. Despite recent advances in diagnostic approaches, mild inherited bleeding disorders still pose a significant diagnostic challenge. Hemorrhagic diathesis can be caused by disorders in primary hemostasis (von Willebrand disease, inherited platelet function disorders), secondary hemostasis (hemophilia A and B, other (rare) coagulant factor deficiencies) and fibrinolysis, and in connective tissue or vascular formation. This review summarizes the currently available diagnostic methods for mild bleeding disorders and their pitfalls, from structured patient history to highly specialized laboratory diagnosis. A comprehensive framework for a diagnostic approach to mild inherited bleeding disorders is proposed.